This invention relates to a valve for a pressurized pack, commonly known as an aerosol can, and particularly to such a valve for dispensing powders from a pressurized pack.
A conventional valve for an aerosol can is illustrated in FIG. 6-1 of "Principles of Aerosol Technology" by Paul A. Sanders, published by Van Nostrand Rheinhold Company, New York. This valve consists of a housing, an elastomeric gasket, a valve stem and a valve spring, the gasket and housing being held together by a mounting flange which also serves to mount the valve in the can. When the valve is closed outlet orifices on the valve stem are sealed by the gasket but when the valve is open these orifices are in communication with the pressurized contents of the can.
The problem involved in producing a satisfactory valve of this type for dispensing powders from a pressurized pack is a considerable one. Particles of the powder become trapped between the sealing surfaces of the valve, reducing the effectiveness of the seal obtained and leading eventually to leakage and loss of pressure in the pack.
A number of attempts at solving this problem have been made and some of the resultant valves have been used commercially. However, none has been entirely satisfactory. In some cases it has been necessary to adopt a discontinuous flew system to avoid leakage problems. This approach is inherently unsatisfactory from the consumers' point of view.